[DeTomaso] Piston Ring Rotation.
Asa Jay Laughton
asajay at asajay.com
Sat May 26 22:27:14 EDT 2012
I've created an illustration of the piston compression ring gaps on the
disassembly of my old Mach I engine.
http://www.teampanteraracing.com/index.php?option=com_g2bridge&view=gallery&Itemid=57&g2_itemId=4970
In that same gallery I've posted a few photos of the main bearings and
other wear.
Asa Jay
Asa Jay Laughton, MSgt, USAFR, Retired
& Shelley Marie
Spokane, WA
******************************
http://www.racingagainstautism.com
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On 5/26/2012 11:58 AM, Asa Jay Laughton wrote:
> Most of us are aware of the proper ring positioning when assembly an engine:
> http://www.351c.info/gallery2/d/218-1/ringspacing.jpg
> The two compression rings should be spaced about 30* (or about one inch)
> from the front centerline of the piston, one on either side. The oil
> ring segments are the same on the opposite side of the piston toward
> the rear. The illustration above shows this quite well.
>
> But do the rings rotate after assembly?
>
> A few years ago at the POCA Fun Rally, Jack had an expert who was
> familiar with pistons. He said indeed the rings do rotate, so in the
> end it doesn't really matter where you index them to start with...
> they're going to move.
>
> Today I recorded the ring locations on my forensics engine. I had been
> careful not to turn the rings on the pistons when I removed the
> pistons/rods from the engine previously. Because I can't insure they
> didn't move at all, the relationships below are rounded. Here are the
> results. My "timing" is from the -front- of the engine, moving
> clockwise. The piston position at 12 o'clock is the part facing front,
> the position at 6 o-clock is at the rear.
>
> The first compression ring is at the top, the second on the bottom.
>
> Piston 1st Comp 2nd Comp Oil/Oil
> #1 8 o-clock 4 o-clock 4/2
> #2 10 11 12/3
> #3 10 2 10/1 (probably the only one closest
> to installed)
> #4 8 8 8/8 (All ring gaps were lined up)
>
> #5 9 2 5/5
> #6 12 9 5/5
> #7 5 4 6/5
> #8 9 3 3/7
>
> As you can see, they are all over the place. I'll work up a good
> illustration and post it later.
>
> Does this mean I won't index them the next time I assemble and engine?
> Actually, I'll most likely still index them when assembling, only
> because I'm anal about those things and I do believe spacing them does
> assist with initial break in. If they are spaced the same, I look at
> that as an easy path for compression gasses to get past. In other
> words, gases might get past the lower tension oil ring segments and past
> the gap in the bottom compression ring but then they'll have to travel
> around the edge a while before they meet up with the gap in the upper
> ring. In the end, it may not really matter.
>
> Asa Jay
> Pantera Research Institute, Pacific Northwest
>
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